A fire wall is a particular class of building construction wall. Section 705 of the 2003 International Building Code, incorporated herein by reference in its entirety, states in general that each portion of a building separated by one or more fire walls that comply with the provisions of Section 705 shall be considered a separate building. The extent and location of such fire walls shall provide a complete separation. Where a fire wall also separates groups that are required to be separated by a fire barrier wall, the most restrictive requirements of each separation shall apply. Fire walls located on lot lines shall also comply with Section 503.2 of the 2003 International Building Code. Such fire walls (party walls) shall be constructed without openings. Fire walls shall have sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall for the duration of time indicated by the required fire-resistance rating. Typical fire resistance ratings are 2 hours, 3 hours or 4 hours.
Another class of building wall is termed “fire barriers”. Section 706 of the 2003 International Building Code, incorporated herein by reference in its entirety, states in general that fire barriers for separation of shafts (also known as shaft walls), exits, exit passageways, horizontal exits or incidental use areas, to separate different occupancies, to separate a single occupancy into different fire areas, or to separate other areas where a fire barrier is required elsewhere in the 2003 International Building Code or the International Fire Code, shall comply with Section 706 of the 2003 International Building Code. Typical fire resistance ratings for fire barriers are 1 hour, 2 hours, 3 hours and 4 hours.
Local building codes and national standard practices require steps be taken in commercial and residential construction to slow the spread of fire through attics, crawlspaces, and other interior locations. Thus, where a fire wall (also known as an area separation wall or party wall) is specified for commercial or residential construction, materials and constructions are employed to meet these specifications. Fire walls or other fire resistive assemblies may be vertical or horizontal. For example, ceilings and sidewalls of a garage adjacent to the dwelling portion of a residential home are typically fire walls or fire barriers.
Residential fire walls or other fire resistive assembly systems meet three structural considerations. First, they form two separate membranes so that, in a fire, one side can collapse without compromising the entire fire barrier. Second, the walls typically have details that insure that if the adjacent structure collapses in a fire, the fire wall will not collapse. Third, the walls are designed for a uniform lateral load of 5 psf to insure lateral stability.
Residential fire walls offer important, specialized construction to protect occupants from fire in multifamily townhouses and other attached dwellings. Not only should these assemblies provide rated fire protection, usually 2 hours, but they must also be designed to be structurally stable enough to withstand the collapse of an adjacent structure without losing their integrity as a wall.
Masonry has long been considered an acceptable material for residential fire walls because of its hardness and perceived strength. An alternative is comparably fire-rated gypsum drywall assemblies.
In addition to the above-discussed International Building Code, two principal code bodies that address the area separation-type fire/party walls are BOCA (See BOCA National Building Code/1990, Section 907.0.)—Building Officials & Code Administrators International Inc. and SBCCI (See SBCCI Standard Building Code/1988 Paragraph 403.5.)—Southern Building Code Congress International. These code bodies identify such assemblies in their codes as either “fire wall,” “party wall” or “townhouse separation wall” or “area separation wall”. Each has essentially the same structural requirement:
“Such wall shall be continuous from the foundation to the underside of the roof sheathing . . . [or shall penetrate through the roof as a parapet].” (See BOCA National Building Code/1990, Section 907.0) and “Walls shall have sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall . . . ” (See SBCCI Standard Building Code/1998 Paragraph 403.5).
For additional guidance, a widely accepted reference document is that of the National Concrete Masonry Assn. (NCMA), TEK 95, “Design Details for Concrete Masonry Fire Walls.”
This document recommends either a double wall or a single wall laterally supported for stability unless designed as a self-supporting cantilever. The document further states the wall be designed to withstand a uniform lateral load of 5 lb./sq. ft. (See NCMA-TEK 95, “Design Details for Concrete Masonry Fire Walls”). The double wall comprising two separate fire-rated walls is most frequently used in load-bearing situations since the fireside portion of the double wall can collapse with the adjoining structure leaving the opposing fire wall in place.
However, the common masonry fire wall configuration separating residential wood-frame construction is the single wall in a non-load bearing mode as a divider between the wood-frame construction on each side. Lateral support can be provided to stabilize the wall at intermediate floors and roofs but the lateral attachment to the structure is designed so that collapse of the fire-side structure will not cause the fire wall to fail.
The fire wall is not an impenetrable buttress as many expect, for a 5 lb./sq. ft. lateral design load (the stated recommendation of the NCMA-See NCMA-TEK 95, “Design Details for Concrete Masonry Fire Walls”) is no different than that of a common interior wall. Also, it is noteworthy to recognize that the code does not require resistance to collapse of the adjacent structure into the fire wall but rather that the fire wall remain standing after collapse.
A common field construction practices is the use of unreinforced hollow concrete masonry. These masonry fire walls are often cantilevered off the foundation without any lateral support at intermediate floors or roof. As a result they may not meet the required 5 lb./sq. ft. lateral load design when erected to necessary building heights. For instance, at a design load of 5 lb./sq. ft. the wall height capacity of unreinforced hollow 8-in. concrete masonry units (CMUs) is about 10.3 ft. (Calculated. Design assumptions: cantilevered; allowable flexural tensile stress 23 lb./sq. in., increased one-third for wind; 100 lb./cu. ft. hollow block, Section Modules S=81 (8-in. CMU) and 160 (12-in. CMU) per NCMA-TEK 2A, “Sizes and Shapes of Concrete Masonry Units”) when free standing as a cantilever and 18.0 ft. (See NCMA-TEK 63, “Partially Reinforced Concrete Masonry Walls”) when simply supported at roof or intermediate floor. If 12-in. CMUs are used, the heights increase to only 14.7 ft. (Calculated. Design assumptions: cantilevered; allowable flexural tensile stress 23 lb./sq. in., increased one-third for wind; 100 lb./cu. ft. hollow block, Section Modules S=81 (8-in. CMU) and 160 (12-in. CMU) per NCMA-TEK 2A, “Sizes and Shapes of Concrete Masonry Units”) and 25.4 ft. (See NCMA-TEK 95, “Design Details for Concrete Masonry Fire Walls”) respectively. See Maurice J. Marchello, Gypsum Fire Wall's Efficiency Gives it Performance Edge, Form and Function, Issue 3 (1990) (also available at http://www.usg.com/Design_Solutions/2—2—8_separationwall.asp).
A masonry cavity fire wall is described in Technical Notes 21, Brick Masonry Cavity Walls, Technical Notes on Brick Construction, Brick Industry Association, Reston, Va. (August 1998). FIG. 1 shows an embodiment of such a cavity wall 1. Brick masonry cavity walls have two wythes of masonry separated by an air space connected by corrosion-resistant metal ties. The exterior masonry wythe 4 can be solid or hollow brick, while the interior masonry wythe 2 (shown as cinderblock) can be solid brick, hollow brick, structural clay tile, or hollow or solid concrete masonry units. The selection for each wythe depends on the required wall properties and features. A cavity of a spacing SS of 2 to 4½ in. (50 to 114 mm) between the two wythes 2, 4 may be either insulated (rigid board insulation 3 shown) or left as an air space. A clearance of a minimum distance S of 1 inch (2.5 mm) is provided between the rigid board insulation 3 and outer wythe 4. The interior surface of the cavity wall 1 may be left exposed or finished in conventional ways. The outer wythe 4 may be provided with weep holes 6. Flashing 7 may also be provided.
Some parts of the country use the term “reinforced cavity walls” to denote a multi-wythe masonry wall with grout placed between the wythes. This should actually be considered a multi-wythe grouted masonry wall. Since the definition of a cavity wall includes an air space, this type of wall is not truly a cavity wall.
Fire resistance ratings of brick masonry cavity walls range from 2 to 4 hours, depending upon the wall thickness and other factors. Due to their high fire resistance properties, brick walls are useful as fire walls or building separation walls for compartmentation in buildings. By using compartmentation, the spread of fire can be halted. Technical Notes 16, Fire Resistance Cavity Walls, Technical Notes on Brick Construction, Brick Industry Association, Reston, Va. (April 2002) describes fire ratings and applicable design conditions.
Some important ASTM standards to understand are ASTM E-119 and C-36. ASTM E 119, Test Methods for Fire Tests of Building Construction and Materials, is the test standard that provides the hourly resistance ratings for wall, floors, roofs, beams, and columns based on adherence of fire exposure to a time-temperature curve. ASTM E-119 is a fire testing method in which an assembly must resist the fire exposure described for the desired classification time without passage of flame or gases hot enough to ignite cotton waste on the non-fire side. The method also entails a specific temperature rise during the test and a second partition specimen that must resist the effects of a hose stream after a fire test of one-half the time duration of the first test. Under E-119, wall and partitions having a fire rating of one hour or more must also be subjected to a hose stream test. The hose stream test has nothing to do with fire fighting practices or strategies. It is actually a convenient way to measure an assembly's ability to withstand lateral impact from falling debris during the fire endurance period and before active fire suppression efforts begin.
ASTM C-36 defines the standards for gypsum board (the product rather than a system containing gypsum board). The C-36 standard entails a variety of product standards that the product must be tested to meet, including composition of various types of gypsum board, flexural strength, humidified deflection, hardness, nail-pull resistance and dimensions. Although the only fire-related characteristics regular core gypsum board must have in ASTM C-36 are a noncombustible core and a maximum flame spread classification of 25, type “X” board, referred to as “special fire-resistant,” must meet specific fire-resistance standards.
To meet the ASTM C-36 standard for ½-in. type ‘X’ board, an assembly using the ½-in. type ‘X’ board on both sides of a load-bearing wood-stud wall must withstand an ASTM E-119 method fire test for 45 minutes. To meet the standard for ⅝-in. type “X” board, a similar assembly with ⅝-in. type “X” board must withstand a similar fire test for 1 hour.
Fire walls may be load bearing or non-load bearing. Unless otherwise noted, a load bearing wall is tested with a constant superimposed load applied to the specimen throughout the fire test to simulate 78% or more of the maximum allowable design load per the Fire Resistance Design Manual—Gypsum Systems, 17th edition, p. 8 Gypsum Association (2003).
An alternative way of determining the fire resistance of a cavity wall assembly is by using the calculated fire resistance method. This approach is approved by the model building codes for determining fire ratings of walls that are not physically tested by ASTM E 119 Test Methods for Fire Tests of Building Construction and Materials. The fire rating of cavity walls can be calculated using Technical Notes 16B, Calculated Fire Resistance, Technical Notes on Brick Construction, Brick Industry Association, Reston, Va. [June 1991] (Reissued August 1991)
Masonry walls, while having good fire resistance, are heavy. An alternative to masonry construction is to construct fire walls by fastening flat modular units from wood or metal trusses or stud walls.
U.S. Pat. No. 6,226,946 to Stough et al. discloses the modular units, typically fire-rated gypsum board, are abutted edge to edge, and provide a barrier to flame and fire-fighting water. Typically gaps or seams between individual modules are covered to reduce the rate of flame and water penetration through the fire wall.
Two different area separation systems employing gypsum board are cavity-type USG Area Separation and solid-type USG Area Separation Walls.
Cavity-type area separation walls are used as commonly shared party walls and fire barriers with non-load-bearing framing. They consist of USG Steel C-H Studs and 1-in. SHEETROCK® Brand Gypsum Liner Panels set in USG Steel C-Runners and faced both sides with ½-in. SHEETROCK® Brand Gypsum Panels, FIRECODE C Core.
The solid system is built with two 1-in. SHEETROCK® Brand Gypsum Liner Panels installed vertically between 2-in. steel H-studs and C-runners. For sound attenuation and added fire protection, THERMAFIBER SAFB insulation can be added to both area separation wall systems.
Both systems function the same way. The fire resistant gypsum panels provide 2-hr. fire-rated performance (3-hr. rated USG Area Separation Walls systems are also available). The steel studs holding the gypsum panels are attached to the unit's wood framing using aluminum angle clips. When exposed to fire, these “break away” clips melt and break on the exposed side, allowing the burning wood frame to fall away. The fire barrier remains intact to protect adjacent units.
Break away fasteners, for example break away clips, are fasteners which attach fire walls (or fire barriers) to adjacent structures so that, in the event of a fire in the adjacent structure, the adjacent structure can fall away from the fire wall while the fire wall maintains its structural integrity throughout the fire.
Likewise, commercial construction employs fire walls. For example, a basic system has 25-ga., 2-½-in, deep USG Steel C-H Studs, 1-in. SHEETROCK Brand Gypsum Liner Panels (which engage the flanges of the C-H studs) and two layers of ½-in. SHEETROCK Brand Gypsum Panels, FIRECODE C Core. IMPERIAL FIRECODE C Gypsum Panels can be used in place of the SHEETROCK Brand Panels if a veneer plaster finish is desired. The assembly of the system with the stud-flanges engaging the shaft wall liner panels is progressive and permits the entire assembly to be installed from the floor side of the shaft. This basic system is UL classified (UL Designs U 438, U459, U467, U469). The USG Cavity Shaft Walls are covered by all three model building codes (BOCA, ICBO and SBCCI) under National Evaluation Report NER-258. The system has been designed and tested using accepted engineering practices with deflection criteria of L120, L240 and L/360 clear partition heights. Additionally, limiting height tables for the system account for flexural and shear forces. Variations of the system have been fire tested up to 4 hours, including four UL design listings up to 2 hrs. Over the years the system has evolved. An original shaft wall system employed a solid gypsum wall using a steel H-stud. The next generation had a cavity created by using a steel box “T” stud. The next generation system uses a steel C-H stud that is lighter in weight and permits less heat and sound transmission than the previous type stud did.
U.S. Pat. No. 6,694,695 to Collins et al. discloses that, while wooden studs are formed of solid wood, typically having nominal cross section dimensions of two inches by four inches, the much greater structural strength of metal, such as twenty-gauge galvanized steel allows building studs to be employed which are not solid, but rather are hollow and have a channel or “C-shaped” cross section. To conform to the architectural plans and building materials developed over the years based on the use of wooden studs having specific cross sectional dimensions, commercially available metal studs are constructed with the same outer dimensions in which wooden studs have been manufactured for many years. Specifically, metal studs are typically formed of sheet metal bent to encompass a cross sectional area having nominal dimensions of two inches by four inches.
For ease of fabrication the metal studs are formed of sheet metal bent into a generally “U-shaped” cross section and in which a relatively broad central web is flanked by a pair of narrower sides that are bent at right angles to the web or base. The web typically has a uniform nominal width of either four inches or three and one half inches, and the sides of the U-shaped stud typically extend a nominal distance of two inches from the web. To enhance structural rigidity the edges of the sides of the metal stud are normally bent over into a plane parallel to and spaced from the plane of the web. These turned over edges of the side walls thereby form marginal lips which are typically one quarter to one half an inch in width. The finished stud therefore has a generally “C-shaped” cross section.
The overhead beams that extend along the tops of the studs in interior building wall construction have a U-shaped configuration. They are each formed with a horizontally disposed web from which a pair of side walls depend vertically on opposite sides of the web. The side walls embrace the sides of the vertical studs so that the upper extremities of the studs extend perpendicular into the concave, downwardly facing channel formed by the overhead beam. The spacing of the studs along the length of the beam is typically either sixteen or twenty-four inches.
One type of fire wall for commercial structures is known as an area separation fire wall/party wall system. USG Area Separation Fire Walls/Party Walls are used for constructing common walls with fire-resistive protection for adjacent properties. These lightweight, non-load-bearing gypsum drywall assemblies are designed as vertical fire barriers for fire walls and party walls separating occupancies in wood-frame apartments and townhouses. Large-size gypsum panels used in conjunction with steel studs and runners quickly become thin, space-saving walls offering excellent privacy.
Available in two basic systems both providing fire-resistant walls from ground level to roof:
Solid Type, with independently framed interior gypsum panel surfaces both sides of fire wall or party wall. Cavity Type, with integral interior gypsum panel surfaces for commonly shared party walls between apartments. Solid-Type wall has two 1″ thick SHEETROCK Brand Gypsum Liner Panels installed vertically between 2″ USG Steel C-Runners. Panel edges are inserted in 2″ USG Steel H-Studs spaced 24″ on center C-runners are installed at top and bottom of wall and back-to-back between vertical panels at a convenient height above each intermediate floor. H-Studs are attached on both sides to adjacent wood framing at intermediate floors, the bottom chords of attic trusses, and at the roof line with 0.063″ USG aluminum angle clips designed to break away when exposed to fire, thus permitting a fire-damaged structure to fall while the fire barrier remains intact. These USG aluminum break away clips are screw attached to studs and framing.
With aluminum angle clips attached on both sides of 25 gauge H-studs, the assemblies are suitable for spans (between clip angle supports) up to 10′ under 5 psf lateral load without exceeding L/240 allowable deflection (for walls with exterior exposure, see section 3.4 of the specification).
With 2″ THERMAFIBER Sound Attenuation Fire Blankets (SAFB) stapled each side of liner panels, the assembly has obtained a 3 hr. fire resistance rating allowing separate selection and construction of tenant walls. Cavity-Type Wall consists of steel C-H Studs and SHEETROCK Brand Gypsum Liner Panels set in steel runners and faced both sides with SHEETROCK Brand Gypsum Panels, Water-Resistant, FIRECODE C Core. Liner panels, 1″ thick, are erected vertically with ends set into 2-½″ USG C-Runners and edges inserted into specially formed 2-½″ USG Steel C-H Studs. C-runners are installed singly at top and bottom of wall and back-to-back between vertical liner panels on a line above each intermediate floor, the bottom chords of attic trusses, and at roof line. Aluminum clips, which attach the C-H Studs on both sides to adjacent wood framing, break away in the same fashion as with solid-type walls. To improve sound transmission loss, THERMAFIBER SAFB are inserted in the stud cavity and RC-1 Resilient Channels or equivalent may be used to isolate the face layer on the cavity side.
With aluminum angle clips attached on both sides of 212CH25 steel studs, the assemblies are suitable for spans (between clip angle supports) up to 10′ under 5 psf lateral load without exceeding L/240 allowable deflection (for walls with exterior exposure see section 3.4 of the specification).
Components used in these systems are designed to permit temporary exposure to inclement weather during construction. These systems may be used in buildings up to four stories high (44 feet) and with all common floor-ceiling heights found in multi-family housing.
Current USG Area separation wall systems are described in USG publication SA925 09250, Fire Wall/Party Wall area separation wall systems, a copy of which is APPENDIX I of U.S. provisional patent application No. 60/646,996 and incorporated herein by reference in its entirety.
Another important type of fire resistive structure is a shaft wall. Shaft walls are wall that enclose elevator shafts and other vertical shafts in a building. Should a fire occur, firefighters control the use of elevators while the stairwells provide the only means for occupant egress or rescue within a building. These walls must have the strength to withstand lateral loads and provide fire protection. A current shaft wall system is the USG SHEETROCK brand Cavity Shaft wall system. It provides up to 4-hour fire resistance and sound ratings up to 52 STC. It resists intermittent lateral loads and fatigue under cyclic lateral loading which is caused by elevators moving in the shaft. The assemblies are constructed of SHEETROCK brand gypsum liner panels friction fitted into USG SHEETROCK brand C-H studs in a progressive manner with SHEETROCK brand gypsum panels applied to the face. Typical shaft walls in a building include elevator shafts, stairwells, mechanical shafts (HVAC, plumbing, electrical, etc.), horizontal membranes or metal duct enclosures, and air return shafts (unlines).
Additional information on current USG shaft wall systems is provided by USG publication SA926 09250 Shaft Wall Systems, a copy of which is APPENDIX II of U.S. provisional patent application No. 60/646,996 and incorporated herein by reference in its entirety.
U.S. Pat. No. 6,620,487 to Tonyan et al., incorporated herein by reference in its entirety, discloses a reinforced, lightweight, dimensionally stable structural cement panel (SCP) capable of resisting shear loads when fastened to framing equal to or exceeding shear loads provided by plywood or oriented strand board panels. The panels employ a core of a continuous phase resulting from the curing of an aqueous mixture of calcium sulfate alpha hemihydrate, hydraulic cement, an active pozzolan and lime, the continuous phase being reinforced with alkali-resistant glass fibers and containing ceramic microspheres, or a blend of ceramic and polymer microspheres, or being formed from an aqueous mixture having a weight ratio of water-to-reactive powder of 0.6/1 to 0.7/1 or a combination thereof. At least one outer surface of the panels may include a cured continuous phase reinforced with glass fibers and containing sufficient polymer spheres to improve nailability or made with a water-to-reactive powders ratio to provide an effect similar to polymer spheres, or a combination thereof. However, U.S. Pat. No. 6,620,487 contains no teaching to specifically employ these shear panels in a fire wall system.
U.S. Pat. No. 6,241,815 to Bonen, incorporated herein by reference in its entirety, also discloses formulations useful for SCP panels.
U.S. patent application Ser. No. 10/666,294, incorporated herein by reference, discloses a multi-layer process for producing structural cementitious panels (SCP's or SCP panels), and SCP's produced by such a process. After one of an initial deposition of loosely distributed, chopped fibers or a layer of slurry upon a moving web, fibers are deposited upon the slurry layer. An embedment device mixes the recently deposited fibers into the slurry, after which additional layers of slurry, then chopped fibers are added, followed by more embedment. The process is repeated for each layer of the board, as desired.
There is a need for an improved economical, easy to assemble, durable and non-combustible total fire wall system.